<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script type="text/javascript" src="jquery-2.1.3.min.js"></script>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        #bg{
            height: 1000px;
            background-color: aqua;
        }
        #model{
            display: none;
            background-color: white;
            position: fixed;
            left: 50%;
            top: 50%;
            margin-left: -200px;
            margin-top: -100px;
            width: 400px;
            height: 200px;
        }
    </style>
    <script>
        function show(){
            var model = $("#")

        }
    </script>
</head>
<body>
<div id="bg">
    <button onclick="show()"></button>
</div>
<div id="model">
    <button>确定</button>
    <button>取消</button>
</div>
</body>
</html>